OCR A-level Biology- communicable diseases

what is a pathogen

a harmful microorganism that causes disease

what are the 4 types of pathogen

bacteria, virus, Protoctista and fungi

what is the bacterial mode of action

producing toxins

what is the viral mode of action

invading host cells and injecting their genetic material within them

what is the protoctistal mode of action

taking over the cells and breaking them open

what is the fungal mode of action

producing toxins which digest and destroy living cells

what is a communicable disease

a disease which can be transmitted between organisms

what type of pathogen causes tuberculosis and what is tuberculosis

bacteria damage lung tissue

what pathogen causes ring rot and in what way

bacteria damages the leaves and fruit

what pathogen causes HIV and how

a virus targets T helper cells

what pathogen causes influenza and how

a virus affects the ciliated epithelial cells

what pathogen causes tobacco mosaic virus and how

a virus damages the leaves, flowers and fruit preventing growth

what pathogen cause malaria and how

a Protoctista invades red blood cells, the brain and the liver

what pathogen causes potato blight and how

a Protoctista destroys the leaves, tubules and fruit

what pathogen causes athletes foot and ow

a fungus causes ring worm between the toes

what pathogen causes Black Sigatoka

a fungus attaches to the leaves and inhibits photosynthesis

what is direct transmission

the passing of a pathogen from host to a new host with no intermediary

what is indirect transmission

the passing of a pathogen from host to a new host via an intermediate

what is disease transmission

the transfer of a pathogen from an infected host to an uninfected host

what are some physical plant defences

thorns/spines/bark/cell wall/thick waxy cuticle/drooping leaves

what are some chemical plant defences

produce toxins/antibacterial compounds

how does a plant detect an infection

cell membrane receptors detect the pathogen and send a message to the nucleus to switch on certain genes

how does a plant use callose to respond to a pathogen

callose is deposited on the plasmodesmata, between the cell wall and cell membrane and blocks holes in sieve plates

how does a plant use lignin to respond to a pathogen

lignin is deposited on the cell wall to provide strength

what are some examples of chemical defences in plants

antibacterial compounds like tea tree oil/saponin which destroys the cell membrane/phytoalexin which inhibits the growth of pathogens

what are some bodily defences in animals/humans

enzymes within tears/ear wax/skin/stomach acid/plateletes/blood clotting/coughing/sneezing

what is the role of cytokines

they’re involved in cell signalling of an attack and resetting the hypothalamus

what is the role of opsonins

to tag pathogens for cell recognition

what are the two types of phagocyte

neutrophils and macrophages

what happens during the inflammatory response to pathogens

mast cells, histamines and cytokines are released

what is a major histocompatibility complex

glycoproteins that bind to antigens and present them on the cell surface membrane of macrophages

whats an antigen presenting cell

a macrophage with antigens on it’s surface to alert other cells of the attack

what do histamines do

dilate blood vessels causing localised heat and redness to reduce pathogen production, more leaky walls increase tissue fluid and white blood cells

describe the process of phagocytosis

the macrophage recognises the pathogen as foreign, the macrophage engulfs the pathogen into a phagosome, the phagosome fuses with a lysosome forming a phagolysosome, MHC presents the antigen becoming an APC to alert other cells to the infection

where do T lymphocytes mature

in the thymus

where do B lymphocytes mature

in bone marrow

what is the function of T helper cells

they trigger the immune response producing antibodies and interleukins

what do T regulator cells do

they supress the immune system

what do T killer cells do

they destroy cells by releasing perforin and hydrogen peroxide which makes holes in the pathogen membrane

what do memory cells do

recognise the antigen

what do B plasma cells do

produce antibodies, opsonins, agglutinins and antitoxins

what do B effector cells do

they detect the attack and develop into plasma cells

what happens in clonal selection

the antigen on the APC is matched with antigen receptors on B or T lymphocytes

what happens in clonal expansion

the cells selected during clonal selection divide by mitosis

what are the structural features of antibodies

heavy chain, light chain, disulphide bridge, hinge region, variable region, constant region

what is agglutination

when two pathogens clump together

what is immunity

resistance to a pathogen through the production of antibodies

what is active immunity

when the body is exposed to the pathogen causing the production of antibodies

what is passive immunity

when the body doesn’t produce antibodies itself

what is an example of natural passive immunity

when antibodies pass through breast milk

what is an example of artificial passive immunity

monoclonal antibodies

what is an example of active artificial immunity

when vaccination triggers an immune response

what body part is affected in rheumatoid arthritis

the joints, especially in hands, wrists, ankles and feet

what body part is affected in type 1 diabetes

the insulin-secreting cells in the pancreas

what body part is affected in lupus

any organ can be attacked but it often affects skin and joints and causes fatigue

what are antibiotics

substances that inhibit the synthesis of bacterial cell wall/bacterial DNA replication

what causes antibiotic resistance

a random mutation/not finishing a course of antibiotics/the overprescription of antibiotics

what is herd immunity

when a large proportion of a population become immune to a disease